* {
  margin: 0;
  padding: 0;
  text-decoration: none;
  box-sizing: border-box;
  list-style: none;
  transition: .3s;
}
.container {
  width: 1200px;
  margin: 0 auto;
}
.header {
  width: 100%;
  height: 90px;
  background-color: pink;
}
.logo {
  width: 140px;
  height: 50px;
  margin-top: 20px;
  float: left;
}
.logo img {
  width: 50px;
  height: 50px;
  float: left;
}
.logo .s {
  float: left;
  margin-left: -15px;
  margin-top: -10px;
  width: 20px;
  height: 20px;
  background-color: red;
  color: #fff;
  border-radius: 50%;
}
.logo .b {
  height: 50px;
  line-height: 50px;
  color: red;
}
nav {
  float: right;
}
ul li {
  float: left;
  margin-right: 20px;
  height: 90px;
  line-height: 90px;
  width: 50px;
}
ul li a {
  color: red;
  font-weight: 700;
  opacity: .5;
}
ul li:hover a {
  opacity: 1;
}
.mask {
  width: 100%;
  height: 100%;
  position: fixed;
  background-color: black;
  z-index: 20;
  perspective: 500px;
}

.dimension {
  width: 500px;
  height: 500px;
  position: relative;
  margin: 200px auto;
  transform-style: preserve-3d;
  backface-visibility:hidden;
  
}
.dimension:hover {
  transform: rotateY(180deg);
}
.dimension div {
  position: absolute;
  width: 100%;
  height: 100%;
  border-radius: 50%;
}
.just {
  background-color: red;
  z-index: 1;
}
.back {
  background-color: blue;
  transform: rotateY(180deg);
}
.main {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}
h1 {
    font-size: 60px;
    color: #6500d2;
    margin-top: 200px;
    margin-bottom: 80px;
    text-align: center;
}
.s1 {
  font-size: 40px;
  color: #000;
  text-decoration: none;
  background-color: skyblue;
  margin-bottom: 20px;
  width: 250px;
  height: 100px;
  text-align: center;
  line-height: 100px;
  border-radius: 20px;
}
